1. Field
The disclosed concept relates generally to circuit interrupters, and more particularly, to circuit interrupters sensitive to current direction.
2. Background Information
Existing photovoltaic (PV) systems employ direct current (DC) fuses and circuit breakers in combiners, re-combiners and inverters to provide over-current protection. However, current DC fuses and circuit breakers do not provide effective protection for PV systems. PV systems have relatively low forward short circuit current levels and potentially high back-feed reverse short-circuit current levels. Both DC fuses and circuit breakers depend on thermal trips to activate the DC fuses or to trip the circuit breakers. Even though these circuit breakers also have magnetic trip, they usually will be activated only at relatively high fault current levels such as 5 times the rated current or higher. The traditional thermal-magnetic trips in a PV system have some disadvantages. One disadvantage is that it can take hours for a thermal trip to activate a DC fuse or cause a circuit breaker to trip. Another disadvantage is that a thermal trip is not sensitive to the direction of the current flowing through the DC fuse or circuit breaker. A relatively low level forward short circuit current in a PV system does not threaten the wiring of the PV system and this condition does not necessarily warrant interrupting the circuit. However, a trip should be quickly initiated for a relatively low level reverse back-feed current in a PV system. Therefore, it would be desirable to provide current direction sensitive circuit protection in PV systems.
Some existing circuit breakers are sensitive to the direction of the current flowing through the protected circuit. However, such circuit breakers generally require additional electronics such as a current sensor or an electronic trip unit which increases the cost of the circuit breaker. It would be desirable to provide current direction sensitivity in a circuit breaker without the need for additional electronics.
There is room for improvement in circuit interrupters.
There is also room for improvement in PV systems employing circuit interrupters.